Microwave-enhanced reactions under open and closed vessel conditions. A case study

Important differences have been observed when performing microwave-enhanced organic transformations, using open and closed vessel conditions. For the hydrolysis of benzamide with sulfuric acid in sealed vessels, where no volatile products are formed, no appreciable difference in reaction performance as a function of the filling volume of the vials or the reaction scale were detected. However, in the cyclocondensation of tetrahydroquinoline with substituted malonic esters, where 2 equiv. of ethanol are formed, the outcome of the reaction under sealed vessel conditions is critically dependent on the scale of the reaction.